Renal organic anion transport is less in newborn than in adults. Transport capacity can be pharmacologically enhanced by administration of substrates of the transport system such as penicillin. We plan to use the tool of substrate stimulation to elucidate the basic biochemical and biophysical steps in organic anion transport. Studyes are designed to correlate uptake and metabolism of fatty acids and other substrates with anion transport. Changes in metabolism associated with changes in PAH transport could be important points of interaction between the anion transport system and uptake of energy substrates. Similar studies with radiolabelled amino acids should provide information relative to proteins involved in organic anion transport.